The role of cyclic AMP-dependent protein kinase and endogenous phosphate acceptor protein in the pathogenesis of hypertension will be evaluated. Cardiac and vascular tissues from spontaneously hypertensive rats (SHR) and Kyoto Wistar normotensive rats (NWR) between 3 to 4 & 12-16 weeks of age will be used in the determination of levels cyclic AMP-dependent protein kinase and its endogenous protein substrate to investigate if any of thise changes precede before the onset of hypertension. Phosphorylation of the endogeneous acceptor protein by the protein kinase influences calcium metabolism and hence it mediates its effects on the muscle contratility. Experiments have been designed to evaluate the differences in cardiovascular muscles of 12-16 week of SHR and NWR in: (a) characteristics of endogenous phosphate acceptor protein, (b) the activity and physical properties of cyclic AMP-dependent protein kinase and its ability to phosphorylate the endogenous membrane substrate, and (c) the properties of isolated kinase subunits and its heterologously and homologously reconstituted holoenzymes.